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Seismic Assessment of Cut and Cover Tunnels

The use of precast and cast-in-place cut and cover tunnels, particularly in urban areas, is increasing in California. Seismic performance of such buried structures is critical in the overall post earthquake availability for the transportation systems. Placing these tunnels on competent or soft and liquefiable soils and covering them with a variety of backfill soils may create a varying seismic response. Seismic ground-tunnel interaction mechanisms are dictated by geometry, stiffness characteristics, and deformation mechanisms of the underground conduit and the surrounding soil. Large-scale shake table testing of representative configurations will provide data sets of seismic response that provide a physical basis for: (1) development of assessment approaches; (2) development and calibration of analytical and numerical models; and (3) development of design guidelines. Such large-scale experimentation allows for employing actual field construction procedures, soil materials, and soil placement/compaction methods. As such, the culvert/tunnel reinforced concrete and/or metallic configuration, and its interaction with the surrounding soil can be represented with a high level of detail. An experimentally validated procedure is needed for seismic assessment of cut and cover tunnels to be used in the seismic analysis and design of these structures.